It depends. The flash storage is faster on the MBP, but it has much worse graphics. The MBP has an i7 vs a newer generation i5 at a higher clock. For most tasks the iMac will be faster. I think the rMBP has double the RAM as the default.
I don't think the iMac will get an update because there are no new chips for it to use. It's already on Skylake and Kaby Lake isn't ready. The good news is that it's not as outdated as the MBP and KL isn't much of an update.
Yeah, no:
Whoever this analyst is, they have the easiest job in the world: Parrot Gurman and Ming!